With the Supreme Court set to rule on gay marriage, 53 senators voted for the amendment sponsored by Sen. Jeanne Shaheen, D-N.H., seven shy of the 60 needed under the rules. Her amendment would have deferred the definition of marriage for qualifying for veterans benefits to the state where the marriage was issued.

Ayotte, Johnson, Portman and Kirk all face competitive reelections in 2016 in states won by President Barack Obama. Ayotte said she supported a similar amendment in the Senate’s budget and that in her opinion, "this is an issue of equal treatment under the law.”

Johnson, who said that he believes marriage should only be between a man and a woman and that it’s for states to decide, noted his vote is just "recognizing the reality of the situation,” with the court’s prior United States v. Windsor ruling.

“It’s basically current law,” Johnson said. "The Supreme Court ruled that same-sex couples qualify for federal benefits. I think it’s putting veterans, who are legally married in a state where it’s legal move to another one, that’s unequal treatment under the law and puts our veterans in a tough position.”

Capito, who also explained her affirmative vote as a matter of fairness, Johnson and Senate Majority Whip John Cornyn, R-Texas, all said this amendment would be moot soon, with an impending Supreme Court decision expected to clarify same-sex marriage nationwide.

Republicans in general have long opposed same-sex marriage, but excluding the moral/religious argument, there’s lots about the amendment that would normally appeal to them, including supporting veterans and states’ rights.

But to Cornyn — with the impending Supreme Court ruling — he viewed Thursday's vote "as more of making a statement than trying to change a policy."

One Democrat, Barbara Boxer of California, and four Republicans, Marco Rubio of Florida, Lindsey Graham of South Carolina, Dean Heller of Nevada and Jerry Moran of Kansas, did not vote.